Osteons are the basic organizational units of spongy bone compact bone bone marrow procalluses

Option B , compact bone

Explanation:

Osteon is the major organizational unit of compact bone. Compact bone is also known as cortical bone which consists of concentric layers of bone called as lamellae. Haverisan canal is lined by these concentric bones which supply blood to the osteocytes. Osteons are parallel thread like structure which are some 0.01  to 0.02  millimeter in diameter and run along the longer bone axis.

Hence, option B is correct.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.